Hydrostatic piston machine comprising a rotatable cam disk

ABSTRACT

The invention relates to a hydrostatic piston machine. The hydrostatic piston machine comprises a housing in which a cylinder drum is rotatably arranged. A first group of cylinder bores and a second group of cylinder bores are arranged in the cylinder drum. Arranged longitudinally displaceably in the cylinder bores are respective pistons, which are supported on a swash plate which may be inclined about at least one swivelling axis. The first group of cylinder bores is temporarily connected to a first hydraulic circuit via first control slots ( 50, 51 ) of a control plate, when the cylinder drum is rotated. Accordingly, the cylinder bores of the second group are temporarily connected to a second hydraulic circuit via second control slots ( 57, 58 ) of the control plate ( 32′ ), when the cylinder drum is rotated. The relative position of the first and/or second control slots ( 50, 51; 57, 58 ) may be altered relative to the at least one swivelling axis of the swash plate.

The invention relates to a hydrostatic piston machine which is provided for delivery in two hydraulic circuits.

For different applications it may be advantageous to provide a hydrostatic piston machine which is connected to two separate hydraulic circuits. In this connection, in a pump of such a configuration it is particularly advantageous to be able to alter separately the volumetric displacement for the two different hydraulic circuits. Such an axial piston machine is known from DE 103 58 728 A1. The axial piston machine comprises a cylinder drum arranged rotatably in a housing. A first group of cylinder bores, as well as a second group of cylinder bores, are arranged in the cylinder drum. Respectively arranged in the cylinder bores are longitudinally displaceable pistons which are supported on a swash plate for producing a piston stroke.

The swash plate may be inclined about a first swivelling axis and about a second swivelling axis, so that the volumetric displacement may be adjusted for the first and second hydraulic circuit. The first and the second swivelling axis are preferably perpendicular to one another. Accordingly, control slots are arranged in a control plate which allows the two-part connection of the cylinder bores to the connections of the first and/or the second hydraulic circuit. The two control slots for the first group of cylinder bores and the two control slots for the second group of cylinder bores are, therefore, rotated by 90° relative to one another, so that one respective inclination about the first swivelling axis produces an alteration to the volumetric displacement in the first hydraulic circuit and an inclination of the swash plate about the second swivelling axis produces an alteration to the volumetric displacement in the second hydraulic circuit.

In the axial piston machine known from DE 103 58 728 A1 it is a drawback that the arrangement of the first control slots and the second control slots relative to one another is predetermined in a fixed manner. In particular, the position thereof is also fixedly set relative to the swivelling axes. In the event that a delivery flow is to be produced not just in the first or in the second hydraulic circuit by the pump, the pistons exceed their top and/or bottom dead centre, whilst the corresponding cylinder bore communicates with one of the control slots. This leads to an undesirable reduction of the efficiency. In order to avoid this, in particular for the simultaneous adjustment of the volumetric displacement in the first and in the second circuit, an adaptation of the position of the first control slots and the second control slots relative to one another as well as to the position of the resulting inclination of the swash plate might be required.

The object of the invention is, therefore, to provide a hydrostatic piston machine which is improved with regard to its efficiency with simultaneous delivery in the first and the second circuits.

The object is achieved by the hydrostatic piston machine according to the invention with the features of claim 1. The sub-claims contain advantageous developments of the invention.

The hydrostatic piston machine according to the invention comprises a housing in which a cylinder drum is rotatably arranged. A first group of cylinder bores and a second group of cylinder bores are arranged in the cylinder drum. The first group of cylinder bores communicates, via first control slots which are arranged in a control plate and when the cylinder drum is rotated, temporarily with the connections of a first hydrostatic circuit. The first group of cylinder bores is thus connected to a connection on the suction side and/or a connection on the pressure side of the first hydraulic circuit via the first control slot when the cylinder drum is rotated. In a corresponding manner, a second group of cylinder bores which are also arranged in the cylinder drum are temporarily connected via second control slots of the control plate to a second circuit on the delivery side and/or suction side. For generating a volumetric flow, pistons are longitudinally displaceably arranged in the cylinder bores of the first group as well as in the cylinder bores of the second group. The pistons are supported on a swash plate for generating a piston stroke when the cylinder drum is rotated. The swash plate may be inclined about at least one swivelling axis. According to the invention, for adapting the position of the control slots to the position of the top and bottom dead centre predetermined by the adjustment of the swash plate, the position of the control slots may be altered relative to the at least one swivelling axis.

By adapting the position of the control slots relative to the at least one swivelling axis, the control slots may be respectively oriented such that the dead centre regions arranged between the control slots are arranged in the control plate in the region of the top and/or the bottom dead centre of the pistons. As a result, it is achieved that while the cylinder bores of the first and/or the second group are connected to the respective control slots, a pure suction stroke, and/or a pure compression stroke is carried out by the pistons without the pistons exceeding the top and bottom dead centre. The reversal from a suction stroke to a compression stroke in the region of the top and/or the bottom dead centre is thus carried out in a dead centre region of the control plate located between the first control slots and/or between the second control slots.

Advantageous developments of the hydrostatic piston machine according to the invention are explained in the sub-claims.

It is advantageous, in particular, to carry out the alteration of the relative position of the first control slots and the alteration of the position of the second control slots differently. In this connection, moreover, it is advantageous, in particular, to carry out the alteration of the relative position of the first control slots and the alteration of the position of the second control slots in a manner which is interdependent, for example, the angle of rotation of the alteration of the position of the first control slots differing from an angle of rotation of the alteration of the position of the second control slots, but being in a fixed relationship thereto.

According to the application, it may be advantageous in particular to alter the position of the first control slots and the position of the second control slots in the same direction. This means that the rotational direction in which the alteration is carried out of the relative position to the at least one swivelling axis of the swash plate is the same for the first control slots and for the second control slots. In a further application, it may however be advantageous that the interdependent alteration of the position of the first control slots and the second control slots is carried out in opposing directions.

It may also be advantageous to be able to alter the position of the first control slots and the position of the second control slots independently of one another. Such a design may, for example, be advantageous if a motor and/or a cylinder are supplied with pressure medium by the two hydraulic circuits. A further example thereof is the combination of a drive in the first hydraulic circuit with a working hydraulic system in the second hydraulic circuit.

For adapting the relative position of the first control slots and/or the second control slots to the at least one swivelling axis of the swash plate it is advantageous to design the control plate with a first control plate ring and with a second control plate ring. The two control plate rings have different diameters so that, preferably, the second control plate ring is arranged in the first control plate ring and centres said first control plate ring. The first control plate ring thus encompasses the first control slots and the second control plate ring encompasses the second control slots.

A preferred embodiment results when the first control plate ring is configured as a spur gear and/or the second control plate ring is configured as an internal gear wheel, and at least one of the two control plate rings cooperates with a toothing of an adjusting element. In this manner, the adjustment of the relative position may take place either via the first control plate ring or, however, via the second control plate ring. If the first control plate ring is configured as a spur gear and the second control plate ring is configured as an internal gear wheel, an independent adjustment may be additionally carried out, therefore, by one respective adjusting element.

In the event that an opposing adjustment of the first control slots and the second control slots has to be carried out, preferably the first control plate ring is designed as an internal gear wheel of a planetary gear set and the second control plate ring as a sun wheel of the planetary gear set. In this manner, it is sufficient either to displace the first control plate ring or the second control plate ring by an adjusting element. Planet wheels fixed on the housing side transfer the adjusting movement to the respective other control plate ring by reversing the rotational direction.

Preferred embodiments of the hydrostatic piston machine according to the invention are shown in the drawings and are explained in more detail in the following description. In this connection, with reference to FIGS. 1 to 4, generally the mode of operation of a hydrostatic piston machine is firstly explained according to the prior art, which is provided for delivering pressure medium in two separate circuits, in which:

FIG. 1 shows a sectional view of an axial piston machine for delivery in two separate hydraulic circuits;

FIG. 2 shows an enlarged view of the drive mechanism of the axial piston machine according to FIG. 1;

FIG. 3 shows a diagrammatic view comprising a swash plate inclined about a first swivelling axis;

FIG. 4 shows a diagrammatic view comprising a swash plate inclined about a second swivelling axis;

FIG. 5 shows a diagrammatic view of an adjustable control plate for a hydrostatic piston machine;

FIG. 6 shows a diagrammatic view of the rear face of the adjustable control plate shown in FIG. 1;

FIG. 7 shows a second embodiment for an adjustable control plate and

FIG. 8 shows a third embodiment for an adjustable control plate.

Before an actual conversion for producing the alteration of the relative position of control slots in a control plate relative to a swivelling axis of a hydrostatic piston machine is explained, the construction and the function of a hydrostatic piston machine, which is provided for delivering pressure medium in two independent hydraulic circuits, are to be explained first for better understanding.

In the longitudinal section of a hydrostatic piston machine 1 shown in FIG. 1 it is shown how a common drive shaft 2 is mounted by a roller bearing 3 on one end of a housing 4. Additionally, the common drive shaft 2 is mounted in a plain bearing 6 which is arranged in a connecting plate 5, which closes the housing 4 at the opposing end.

An opening 7 is configured in the connecting plate 5 penetrating the connecting plate 5 completely in the axial direction, in which firstly the plain bearing 6 is arranged and which secondly is penetrated by the common drive shaft 2. On the side of the connecting plate 5 remote from the housing 4, an auxiliary pump 8 is inserted in a radial widening of the opening 7. For driving the auxiliary pump 8, the common drive shaft 2 has a toothing 9 which is in engagement with a corresponding toothing of an auxiliary pump shaft 10. The auxiliary pump shaft 10 is mounted in the opening 7 by a first auxiliary pump plain bearing 11 and by a second auxiliary pump plain bearing 12 in an auxiliary pump connecting plate 13.

An auxiliary pump gear wheel 14 is arranged on the auxiliary pump shaft 10 which is in engagement with an auxiliary pump internal gear wheel 15. Via the auxiliary pump gear wheel 14, the auxiliary pump internal gear wheel 15 which is rotatably arranged in the auxiliary pump connecting plate 13, is also driven by the auxiliary pump shaft 10 and thus ultimately by the common drive shaft 2. Configured in the auxiliary pump connecting plate 13 are the connections on the suction side and on the pressure side for the auxiliary pump 8. The auxiliary pump 8 is fixed in the radial widening of the opening 7 of the connecting plate 5 by a cover 16, which is mounted on the connecting plate 5.

The inner race of the roller bearing 3 is fixed in the axial direction on the common drive shaft 2. The inner race bears, on the one hand, against a collar 17 of the common drive shaft 2 and is retained, on the other hand, in this axial position by a locking ring 18 which is inserted into a groove of the common drive shaft 2. The axial position of the roller bearing 3 relative to the housing 4 is determined by a further locking ring 19, which is inserted into a peripheral groove of the shaft opening 20. On the other side the roller bearing 3 bears against a housing shoulder, not shown, of the housing 4. In the direction of the outside of the housing 4 in the shaft opening 20, moreover, a sealing ring 21 and finally a further locking ring 22 are arranged, the locking ring 22 being inserted into a peripheral groove of the shaft opening 20.

On the end of the common drive shaft 2 projecting from the housing 4, a drive toothing 23 is configured, via which the hydrostatic piston machine is driven by a drive machine, not shown.

Arranged in the interior of the housing 4 is a cylinder drum 24 which has a central through-opening 25, which is penetrated by the common drive shaft 2. The cylinder drum 24 is connected to the common drive shaft 2 by means of a driving spline 26 so as to be locked against rotation but displaceable in the axial direction, so that a rotational movement of the common drive shaft 2 is transmitted to the cylinder drum 24.

Inserted into a peripheral groove formed in the central through-opening 25 is a further locking ring 27 against which a first support disk 28 bears. The first support disk 28 forms a first spring bearing for a compression spring 29. A second spring bearing for the compression spring 29 is formed by a second support disk 30, which is supported on the front face of the driving spline 26. The compression spring 29 thus exerts, on the one hand, on the common drive shaft 2 and, on the other hand, on the cylinder drum 24 a force in the respectively opposed axial direction. The common drive shaft 2 is loaded such that the outer race of the roller bearing 3 is supported on the locking ring 19.

The compression spring 29 acts in the opposite direction on the cylinder drum 24 which is retained by a spherical recess 31 configured on the front face of the cylinder drum 24 in abutment against a control plate 32. The control plate 32 bears, in turn, with the face remote from the cylinder drum 24 sealingly against the connecting plate 5. The cylinder drum 24 is centred by means of the spherical recess 31, which corresponds to a matching spherical projection of the control plate 32. The control plate 32 may also be designed as a planar disk if, for example, a centring of the cylinder drum 24 carried out in a different manner with a spherical control plate 32 might lead to redundancy.

Cylinder bores 33 are introduced into the cylinder drum 24, distributed over a common pitch circle, in which pistons 34 are arranged which are longitudinally displaceable in the cylinder bores 33. On the end remote from the spherical recess 31, the pistons 34 project partially out of the cylinder drum 24. At this end, fastened to the pistons 34 is one respective sliding shoe 35, via which the pistons 34 are supported on a bearing surface 36 of a swash plate 37.

For generating a lifting motion of the pistons 34, the angle which the bearing surface 36 of the swash plate 37 encloses with a central axis 40 is variable. To this end, the inclination of the swash plate 37 may be adjusted by an adjusting device 38. The swash plate 37 is supported in the housing 4 for absorbing the forces which are transmitted by the sliding shoes 35 to the swash plate 37.

For connecting the hydrostatic piston machine 1 to a first hydraulic circuit and to a second hydraulic circuit a first connection 39 and a second connection 39′ are shown diagrammatically in the connecting plate 5 which, in a manner not shown, may be connected via the control plate 32 to the cylinder bores 33.

An enlarged view of the components cooperating in the interior of the housing 4 is shown in FIG. 2.

For carrying out a swivelling movement, the swash plate 37 is coupled to a slide block 44 which, in a manner not shown, rotates the swash plate 37 about a swivelling axis located in the drawing plane.

The cylinder bores, generally denoted by 33 in FIG. 1, are divided into a first group of cylinder bores 33.1 and a second group of cylinder bores 33.2. As has already been briefly explained in the embodiments of FIG. 1, one respective sliding shoe 35 is arranged against the end of the pistons 34 remote from the control plate 32. The sliding shoe 35 is fastened by a recess to a spherical head of the piston 34, so that the sliding shoe 35 is movably fixed to the piston 34 and tensile and compressive forces may be transmitted.

Configured on the sliding shoe 35 is a sliding surface 45 by means of which the sliding shoe 35 and thus the piston 34 are supported on the bearing surface 36 of the swash plate 37. Formed in the sliding surface 45 are lubricating oil grooves which are connected via a lubricating oil channel 46, which is configured in the sliding shoe 35 and extended in the piston 34 as a lubricating oil bore 46′, to the cylinder bores 33 configured in the cylinder drum 24.

By supporting the sliding shoe 35 on the bearing surface 36, during the rotation of the common drive shaft 2, the pistons 34 execute a lifting movement between a top dead centre and a bottom dead centre, by means of which the pressure medium located in the cylinder chambers in the cylinder drum 24 is placed under pressure. The sliding shoes 35 are hydrostatically relieved on the bearing surface 36 of the swash plate 37.

In order to deliver the pressure medium from the cylinder chambers into the first and/or second hydraulic circuit, respectively first connecting channels 47.1 and/or second connecting channels 47.2 are connected to the cylinder bores of the first group 33.1 and/or the cylinder bores of the second group 33.2. The first and second connecting channels 47.1 and 47.2 extend from the cylinder bores of the first group 33.1 and/or the cylinder bores of the second group 33.2 to the spherical recess 31, which is configured on a front face 48 of the cylinder drum 24.

Configured in the control plate 32 are first control slots 50 and 51 which penetrate the control plate 32 in the axial direction.

Moreover, second control slots are configured in the control plate 32, which as a result of the position of the cutting plane are not visible in FIG. 2. Whilst the first control slots 50 and 51 are connected via the connecting plate 5 to working lines of the first hydraulic circuit, in a corresponding manner the second control slots are connected to the two working lines of the second hydraulic circuit.

The first control slots 50 and 51 are at an identical first distance R₁ from the central axis 40 of the cylinder drum 24, which is greater than the distance R₂ which, in turn, is identical for the second control slots. During a rotation of the common drive shaft 2, the first connecting channels 47. 1 are connected in succession to the first kidney-shaped control ports 50 and the second kidney-shaped control ports 51, so that as a result of the lifting movement of the pistons 34 arranged in the cylinder bores 33.1 of the first group, the pressure medium is drawn in via the one first control slot 51 and pumped via the other first control slot 50 into the working line of the first hydraulic circuit on the pressure side.

In the embodiment shown, the first connecting channels 47.1 are arranged in the cylinder drum 24, such that the first distance R₁ of the outlet on the front face 48 is greater than the second distance R₂ at which the second connecting channels 47.2 open out on the front face 48. The second connecting channels 47.2 have a radial directional component and accordingly open out on the front face 48 of the cylinder drum 24 at the second distance R₂, which corresponds to the distance of the second control slot from the central axis 40. During a rotation of the common drive shaft 2, therefore, the cylinder bores of the second group 33.2 are alternately connected via the second connecting channels 47.2 to the two second control slots.

In order to prevent the sliding shoes 35 from lifting off the bearing surface 36 of the swash plate 37 during a suction stroke, a retraction plate 52 is provided which encompasses the sliding shoes 35 on a shoulder provided therefor. The retraction plate 52 comprises, for example, a spherical central recess 53 with which it is supported against a retraction ball 54, which is arranged on the end of the cylinder drum 24 remote from the front face 48.

In FIG. 3 it is shown how, proceeding from an axial piston machine of FIGS. 1 and 2, with a swash plate 37′ an independent adjustment of the delivery rates may be achieved for the two hydraulic circuits.

The swash plate 37′ may be inclined about a first swivelling axis 55 and about a second swivelling axis 56. The first and the second swivelling axes 55 and 56 are located in the plane of the bearing surface 36 of the swash plate 37 and, when the axial piston machine is set to zero volumetric displacement in both hydraulic circuits, enclose an angle of 90° with the central axis 40.

In FIG. 3 the swash plate 37′ is shown inclined about the second swivelling axis 56. Thus an effective stroke for delivering pressure medium, for example into the second hydraulic circuit, is produced. The term “effective stroke” in this case denotes a movement of the pistons 34 which leads to an actual delivery of pressure medium.

The second connecting ducts 47.2 move during a half revolution of the cylinder drum 24 from the bottom dead centre to the top dead centre, substantially along the one second control slot 57 so that the pressure medium is forced into the working line of the second hydraulic circuit on the pressure side. During the second half of a revolution of the cylinder drum 24, accordingly the second connecting ducts 47.2 move en route from the top dead centre to the bottom dead centre substantially along the other second control slot 58 and perform a suction stroke.

In the embodiment shown, the first swivelling axis 55 and the second swivelling axis 56 are arranged at right angles to one another.

A delivery into the first hydraulic circuit does not occur with the illustrated deflection of the swash plate 37′. The position of the first control slots 50 and 51 is symmetrical relative to the position of the top and/or bottom dead centre, so that in spite of the use of the common swash plate 37′ in the first hydraulic circuit only one pulsation is produced as long as the swash plate 37′ is not additionally inclined about the first swivelling axis 55.

For a delivery exclusively into the first or the second hydraulic circuit, the first and the second control slots 50, 51, 57, 58 are preferably arranged in the control plate 32 rotated by 90° relative to one another. The second control slots 57, 58 are thus configured to be symmetrical to a projection 56′ of the second swivelling axis 56 into the plane of the control plate 32. The first control slots 50, 51 are accordingly symmetrically configured relative to a projection (not shown) of the first swivelling axis 55. This is, however, a drawback for a variable adjustment of the delivery rates of both circuits.

In the preferred embodiment shown, the first swivelling axis 55 and the second swivelling axis 56 are arranged at right angles to one another, the two swivelling axes 55 and 56 being located in the plane of the bearing surface 36. The point of intersection of the first swivelling axis 55 with the second swivelling axis 56 coincides with the point of intersection of both swivelling axes 55 and 56 with the central axis 40.

On its face remote from the bearing surface 36, the swash plate 37′ is configured to be of hemispherical shape, at least in a region 59 adjoining the bearing surface 36. As a bearing, a ball bearing or a plain bearing may be provided in order to support the swash plate 37′ and to permit the rotation thereof. In order to keep the overall axial length of the axial piston machine as short as possible, the hemispherical region 59 is defined by a flattened portion 63 preferably configured parallel to the bearing surface 36.

The adjustment of the inclination of the swash plate 37′ may be carried out either via a separate adjusting device for each swivelling axis 55 and 56, in FIG. 1 only the adjusting device for the swivelling axis 55 being shown and the adjusting device for the swivelling axis 56 not being visible in the sectional view, or however via a common adjusting device via which a resulting angle of inclination of the swash plate 37′ is set.

In FIG. 4 it is shown that the swash plate 37′ is located in its neutral position relative to the second swivelling axis 56, but is inclined relative to its first swivelling axis 55. Thus an effective stroke is produced only for the pistons 34 which are alternately connected via the first connecting channels 47.1 during a revolution of the cylinder drum 24 to the one first control slot 50 and the other first control slot 51.

Those pistons, however, which may be connected via the second connecting ducts 47.2 to the second control slots 57 and/or 58, in the region in which a connection is made to the respective hydraulic circuit, execute merely one movement about the bottom dead centre and/or about the top dead centre, which in turn produces merely a slight pulsation in the working lines of the second hydraulic circuit.

An embodiment for an adjustable control plate 32′ is shown in FIG. 5. In the perspective view of the control plate 32′ the face of the control plate 32′ oriented toward the connecting plate 5 of the hydrostatic piston machine 1 is shown. The control plate 32′ comprises a first control plate ring 70 and a second control plate ring 71. The first control plate ring 70 and the second control plate ring 71 are arranged in a common plane and together form the control plate 32′. To this end, the external diameter of the second control plate ring 71 is dimensioned such that the second control plate ring 71 may be arranged in a central recess of the first control plate ring 70. In the embodiment shown, the first control plate ring 70 and the second control plate ring 71 form a internal gear wheel and/or a sun wheel of a planetary gear set. For creating a rotational movement on the first control plate ring 70 a first toothing 72 is configured on the outer front face.

A second toothing 73 is configured relative to the internal peripheral edge of the first control plate ring 70 which is set back in the radial direction, over a portion of the depth of the first control plate ring 70. Accordingly, relative to the outer peripheral edge of the second control plate ring 71 which is set back in the radial direction, a third toothing 74 is formed on the second control plate ring 71. Arranged between the second toothing 73 of the first control plate ring 70 and the third toothing 74 of the second control plate ring 71 are planetary gears 75.1, 75.2 and 75.3. For the sake of improved clarity, the bearing arrangement of the planetary gears 75.1, 75.2 and 75.3 is not shown. The planetary gears 75.1, 75.2 and 75.3 are rotatable about their central axes but fixedly arranged in the housing 4 of the piston machine 1.

The two first control slots 50 and 51 are formed on their face facing the connecting plate 5 by four respective control slot portions 50.1 to 50.4 and/or 51.1 to 51.4. Accordingly, the second control slots 57 and/or 58 are formed by control slot portions 57.1 to 57.4 and/or 58.1 to 58.4. First dead centre regions 86 and/or 87 are formed between the control slot portions 50.1 to 50.4 and the control slot portions 51.1 to 51.4. In a corresponding manner, second dead centre regions 88 and/or 89 are formed between the second control slot portions 57.1 to 57.4 and 58.1 to 58.4. In the hydrostatic piston machine according to the invention, the position of said first dead centre regions 86, 87 and/or second dead centre regions 88 and/or 89 are adapted to the top and bottom dead centre positions resulting from the inclination of the swash plate 37.

In the embodiment shown in FIG. 5, the adaptation of the dead centre regions 86, 87 and 88, 89 takes place in opposing directions. The rotational direction of the first control plate ring 70 is, to this end, transmitted in the planetary gear set in which the planetary gears 75.1 to 75.3 are fixedly arranged, in the reverse direction onto the second control plate ring 71.

An adjusting element 76 is provided for producing the drive torque on the first control plate ring 70. In the embodiment shown, the adjustment both of the first adjusting control plate ring 70 and of the second control plate ring 71 is therefore produced by a single adjusting element 76. The adjusting element 76 comprises a shaft 77 which carries, on a first end, a first spur gear 78 and, on its second end, a second spur gear 79. The two spur gears 78 and 79 are connected to the shaft 77 fixedly in terms of rotation which, in a manner not shown, is mounted in the connecting plate 5 of the hydrostatic piston machine 1. A rotational movement of the shaft 77 is transmitted to the first control plate ring 70 via the first spur gear 78 which is in engagement with the first toothing 72 of the first control plate ring 70. The rotational movement of the shaft 77 is produced on the second spur gear 79, the toothing on the front face of the second spur gear 79 cooperating with a gear rack 80.

The gear rack 80 is preferably axially displaceably arranged in the connecting plate 5 and may be acted upon at its two front faces 81, 82, for example by a hydraulic force. The gear rack 80 is preferably mounted sealingly in the connecting plate 5 in the region of its opposing ends through a first guide region 83 and a second guide region 84. Configured on the two front faces 81 and 82, in the connecting plate 5, are pressure chambers, through which the first front face 81 and/or the second front face 82 may be acted upon by a hydraulic force. Depending on an axial force on the gear rack 80, resulting from a difference between the hydraulic forces on the front faces 81 and 82, the gear rack 80 is displaced and produces a rotational movement of the adjusting element 76 which, with the second spur gear 79, is in engagement with a gear rack toothing 85. Within the scope of the maximum axial displacement, therefore, a displacement of the relative position of the first control plate ring 70 and thus of the first control slots 50, 51 relative to the swivelling axis of the swash plate 37 is possible. At the same time, by the formation of the control plate 32′ as a planetary gear set, an opposing alteration to the relative position of the second control plate ring 71 is effected.

The arrangement of FIG. 5 is shown in FIG. 6 from the rear. Thus the face of the control plate 32′ oriented toward the cylinder drum 24 is shown in FIG. 6. It may be seen that the first control slot portions 50.1 to 50.4 and 51.1 to 51.4 on this face are connected to first control slots 50 and/or 51. Accordingly, the second control slot portions 57.1 to 57.4 and/or 58.1 to 58.4 are connected to second control slots 57 to 58. Between the first control slots 50, 51 the first dead centre regions 86′, 871 may be seen clearly and between the second control slots 57, 58 the second dead centre regions 88′, 89′ may be seen clearly. Moreover, it may be seen in FIG. 6 that on the face oriented towards the cylinder drum 24 the internal diameter d₁ of the first control plate ring 70 corresponds to the external diameter D₂ of the second control plate ring 71, so that the first control plate ring 70 is centred on the second control plate ring 71. This is advantageous, in particular, when the internal diameter d₂ of the second control plate ring 71 is dimensioned such that a centring is carried out on the plain bearing 6.

A second embodiment for an adjustable control plate is shown in FIG. 7. In the second embodiment, the first toothing 72 of the first control plate ring 70 cooperates with a first adjusting element 76′. The first adjusting element 76 is driven by the drive element 80 in the same manner as has already been explained with reference to FIG. 5. The dependent adjustment of the first control plate ring 70′ and the second control plate ring 71′ takes place, however, not by forming the first control plate ring 70′ as an internal gear wheel and the second control plate ring 71′ as a sun wheel of a planetary gear set, but by a second adjusting element 90 which directly drives the second control plate ring 71′. The second control plate ring 71′ is, to this end, provided on its inner periphery with a fourth toothing 91 which cooperates with a first spur gear 92 of the second adjusting element 90. In a similar manner to the first adjusting element 76′, the second adjusting element 90 is also constructed with a shaft 93, the first spur gear 92 as well as a second spur gear 94 of the second adjusting element 90 being arranged on the opposing ends thereof. The two adjusting elements 76 and 90 are preferably of identical construction. In order to transfer a rotational movement of the first adjusting element 76 to the second adjusting element 93, the second spur gears 79 and 94 of the first adjusting element 76 and/or of the second adjusting element 90 are connected to one another via a spur gear unit. In the simplest case, the spur gear comprises a single intermediate gear 95. The intermediate gear 95 is also arranged in the connecting plate 5, in a manner not shown. In the preferred embodiment shown, the second adjusting element 90 is adapted to the first adjusting element 76 insofar as the resulting rotational movement of the first control plate ring 70 and of the second control plate ring 71 is identical.

With a suitable choice of gear ratio of the spur gear unit, by the actuation of the drive element 80, different alterations to the position of the first and second control slots 50, 51 and 57, 58 may also be achieved.

In the third embodiment shown in FIG. 8, a single adjusting element 76 and/or 90 is in turn associated with each control plate ring 70′, 71′. In contrast to the embodiment of FIG. 7, for driving the adjusting elements 76 and/or 90 respectively one separate gear rack 80 is provided as a drive element and/or 96. In this case, the second drive element 96 cooperates via a spur gear unit with the further spur gear 95′. With the arrangement shown in FIG. 8 it is possible to adjust the first control plate ring 70 and the second control plate ring 71 completely independently of one another with regard to their relative position to the swivelling axis of the swash plate 37 of the hydrostatic piston machine 1. The impingement of the second gear rack 96 takes place preferably also hydraulically with an actuating pressure in the connecting plate 5.

With the proposed embodiments for adjustable control plates 32′ it is possible to adapt the position of the first and/or second dead centre regions 86, 87, 88, 89 to the respective operating state of the piston machine 1.

Depending on the volumetric displacement set respectively for the first and/or second hydraulic circuit, the resulting swivelling axis, which results from the inclination of the swashplate 37 about the first swivelling axis 55 and the second swivelling axis 56, is variable. Accordingly, the position of the top and/or bottom dead centre of the pistons 34 is altered in the cylinder bores 33.1, 33.2 of the first as well as the second group. By means of the adjustable control plate 32′, according to one of the embodiments of FIGS. 5 to 8, an adaptation of the position of the first control slots 50, 51 and/or the position of the second control slots 57, 58 and thus of the first dead centre regions 86, 87 and/or the second dead centre regions 88, 89 to the position of the top and/or bottom dead centre of the pistons 34 is possible.

The invention is not restricted to the embodiments shown. In particular it is possible to combine individual features of the individual embodiments in any manner with one another. 

1. Hydrostatic piston machine comprising a cylinder drum rotatably arranged in a housing having a first group of cylinder bores which are temporarily connected to a first hydrostatic circuit via first control slots of a control plate, when the cylinder drum is rotated, and having a second group of cylinder bores which are temporarily connected to a second circuit via second control slots of the control plate when the cylinder drum is rotated, pistons being longitudinally displaceably arranged in the cylinder bores which are supported on a swash plate, the swash plate being able to be inclined about at least one swivelling axis for producing a piston stroke, characterised in that the position of the first and/or second control slots may be altered relative to the at least one swivelling axis.
 2. Hydrostatic piston machine according to claim 1, wherein the alteration of the relative position of the first control slots and the alteration of the relative position of the second control slots differ from one another.
 3. Hydrostatic piston machine according to claim 1, wherein the alteration of the relative position of the first control slots and the alteration of the relative position of the second control slots are interdependent.
 4. Hydrostatic piston machine according to claim 3, wherein the position of the first control slots and the position of the second control slots may be altered in the same direction.
 5. Hydrostatic piston machine according to claim 3, wherein the relative position of the first control slots and the relative position of the second control slots may be altered in an opposing manner.
 6. Hydrostatic piston machine according to claim 1, wherein the relative position of the first control slots and the relative position of the second control slots may be altered independently of one another.
 7. Hydrostatic piston machine according to, claim 1, wherein the control plate comprises a first control plate ring and comprises a second control plate ring, the first control slots being arranged in the first control plate ring and the second control slots being arranged in the second control plate ring.
 8. Hydrostatic piston machine according to claim 7, wherein the first control plate ring is configured as a spur gear and/or the second control plate ring is configured as an internal gear wheel, and at least one of the two control plate rings cooperates with a toothing of an adjusting element.
 9. Hydrostatic piston machine according to claim 8, wherein the first control plate ring is an internal gear wheel of a planetary gear set and the second control plate ring is a sun wheel of a planetary gear set.
 10. Hydrostatic piston machine according to claim 8, wherein the internal gear wheel and the spur gear cooperate with toothings of a first adjusting element and/or a second adjusting element.
 11. Hydrostatic piston machine according to claim 10, wherein the first and the second adjusting elements are coupled together by a spur gear unit.
 12. Hydrostatic piston machine according to claim 10, wherein the first and the second adjusting elements are respectively driven by a toothed rack. 